Method of deoxidation control



Patented Feb. 16, 1937 UNITED STATES PATENT OFFICE METHOD OF DEOXIDATION CONTROL Ohio No Drawing. Application November 12, 1931, Serial No. 574,676. Renewed January 24, 1934 3 Claims.

Our invention relates to methods of control of deoxidation in the manufacture of iron and steel. In the past it has been the practice in the manufacture of iron and steel, to add deoxidizing materials to the metal bath pursuant to a rule of thumb practice, which has no real accuracy. It has been attempted to govern the amount of deoxidizing substance by attempting to follow a uniform practice in the refining of the metal charge, and then adding a measured and uniform quantity of deoxidizer per ton of metal. It has been attempted to judge the oxide content of a bath of iron or steel by an examination of the slag, and by an observation of the conditions in the furnace and of the fracture of a sample, etc.

None of these methods are accurate, and particularly when expensive substances are added to a metal bath, which substances are readily oxidizable, it is necessary to know just how much to add or else there will be wastage, or over or under use of the particular material.

If it were possible to attain it, a true analysis of the oxide content of a bath of steel or iron is the only way in which to govern accurately the amount of addition of oxidizable substances which may be or are required to be added thereto. The difliculty with following such a practice is that until our invention, which we now propose to describe, the determination of oxide content of molten metal was a long and delicate task taking hours in the laboratory, and it is obvious that in the making of iron and steel there can be no extended wait in the process after the metal is finished and before tapping, or otherwise treating the metal, so that such an analysis could be made.

We have discovered a mode of analysis for oxygen content in molten iron and steel which can be completed in twenty minutes or less, and is not a delicate or difi'icult operation at all, and hence our invention relates to the control of oxidizable additions to a completed body of iron and steel by a test of the oxide content of the metal itself, carried out by chemical analysis, and preferably according to the steps which we will now outline.

When the refining procedure is substantially complete and the metal is in the condition requiring tapping or deoxidizing, we take a sample of the metal from beneath the slag, this sample being a definite amount, and to this sample we add a predetermined quantity of aluminum, which aluminum is considerably in excess of the amount which will chemically combine with all the possible oxygen in the metal. A convenient weight of drillings is taken from the product of this reaction after cooling the same, and the material,

other than aluminum oxide, is dissolved away. This can be done with a solution of iodine. The iodine solution when heated attacks and quite readily and quickly dissolves the iron and other metals including aluminum, but does not attack aluminum oxide (alumina). When the iron has been dissolved oif (and the remaining, which is alumina residue plus carbon is washed and ignited to dry it and drive off carbon), the remaining material, which is alumina, is weighed. By the formula A1203 and atomic weights of these two elements, the exact weight of the oxygen which was in the drilling is obtained. From this may be obtained the percentage of oxygen present in the drillings andtherefore also in the original bath of iron or steel.

The whole procedure can be completed in less than twenty minutes, and the oxide content will not be materially increased by holding the bath for such a short period; nor will the ability to tap the metal properly and at proper temperature be interfered with.

While the described iodine method seems to be the most suitable because of its rapidity, other dissolving agents may be used giving comparatively quick results, to wit, nitric acid, nitric acid mixed with hydrochloric acid, salts mixed with acids, mixtures of acids with an oxidizing agent in which a halogen is set free.

A method using cold nitric acid which we have successfully employed is as follows:

The sample is prepared for analyses by the same practice used in the iodine method. Ten grams of the sample are dissolved with 200 m. l. of dilute nitric acid (1.2) in a beaker of sufficient size to eliminate any loss of sample due to violent effervescence during solution of the sample. The acid is added carefully to prevent a reaction which is too violent. When the sample is in solution, one hundred and fifty m. l. of cold water are added and the solution is filtered immediately on a fairly retentive filter paper, using suction apparatus if necessary. The residue remaining on the paper is washed first with hot water and then alternately with hot dilute hydrochloric acid (1--1) and water until free from iron salts. The filter paper and residue are transferred to a weighed platinum crucible and ignited to remove the paper and other carbonaceous material. The crucible is weighed. Difference in weight represents aluminum oxide. The oxygen in the aluminum oxide is calculated to per cent oxygen in the material under test and serves as a guide for proper deoxidation.

In this manner we are able to control the amount of substance to be added with exact relationship to the amount of oxygen in the metal to which it is to be added. The addition may be made in accordance with any accepted practice.

It will naturally be possible to use another substance than aluminum, which has a like property of combining with oxygen to make an oxide which resists the action of solvents which will quickly dissolve iron or steel. If an alloy of iron or steel is the product of the finished metal bath and any of the ingredients are insoluble in the iron solvent employed, then allowance will have to be made for them, if the alloying metals are in any amount which would interfere with reaching a sufiiciently accurate percentage.

While we have described our new process in connection with iron and steel, it may be also employed in the deoxidation of other metals such as, for instance, copper and brass.

Having thus described our invention, what we I claim as new and desire to secure by Letters Patent, is:--'

'1. A process for the treatment of iron or steel which comprises refining the iron or steel in the usual way and at the conclusion of the refining process and while maintaining the bath of metal molten, chemically determining the percentage of oxygen therein by taking a determined sample of the material, combining it with an amount of aluminum which is in excess of any amount necessary to combine with the oxygen present inthe sample by chemical combining Weight, then dissolving the iron or steel from the sample, or part thereof of a determined weight, without affecting the alumina, and finally weighing the remaining solid and calculating the weight of oxygen and hence its percentage in the'metal sample and the amount of deoxidizer necessary to bring said metal bathto a desired state of deoxidization, all of said steps being carried on rapidly while said metal bath is maintained molten and in a condition for deoxidization, and then adding deoxidizing agent to said metal bath as determined by said calculation.

2. That method of determining the oxygen content of a mass of molten iron or steel which consists in combining a determined sample with an amount of aluminum which is in excess of an amount necessary by chemical combining weights to combine with the probable oxygen present in the sample, then rapidly dissolving the iron or steel from the sample or a weighed portion, without afiecting the alumina and finally weighing the remaining alumina, calculating the weight of oxygen therein and comparing this with the weight of the sample portion, whereby to determine the oxygen content of said mass of molten iron or steel, all of said steps being carried 'on so rapidly that said determination can be made between the conclusion of the refining process for :said metal and the deoxidization of the same metal.

3. That method of determining the'oxygen content of a massof 'molteniron or steel which consists in combining a determined sample with an amount of aluminum which is in excess of an amount necessary by-chemical combining weights to combine with the probable oxygen present in the sample, then dissolving the iron or steel from the sample, or a'weighed-portion thereof, without affecting the alumina, and finally weighing the remaining alumina, calculating the weight of oxygen therein and comparing this with the weight of the sample portion, said dissolving action being accomplished by the use of hot iodine solution as a solvent. ANSON HAYES.

JESSE J. CANFIELD. 

